Recessed lights, insulation and ventilation

Reply

  #1  
Old 05-27-03, 11:56 AM
A
Member
Thread Starter
Join Date: Mar 2003
Location: Central NJ
Posts: 137
Received 0 Votes on 0 Posts
Recessed lights, insulation and ventilation

I have several questions regarding attic insulation and ventilation.

1. I installed recessed lights that can contact insulation. I need to add insulation to my old house artic. I consider faced batt insulation. How do I put it? Should I just roll batts between joists? Should I staple batts to joists? Recessed lights housing are taller then joists. How do I cover them with insulation? Should I roll bats over the housing or put small pieces of batts between housing and joists?

2. My house is two story colonial, second floor does not fully extend over the first floor. So I have two attics, one over the second floor and another over part of the first floor. On the second floor artic I have fans on both side of artic so that air flows freely through both side of the attic. First floor attic faces the building on one side so the attic is ventilated through only one fan on the side that faces out the house. I think air does not flow good through first floor attic so the living room on the first floor under the attic is getting hot on summer, actually hotter then rest of the first floor. What would be a solution for that? Also what fan size and power should I use in attics? The fans I have are very old.
 
Sponsored Links
  #2  
Old 05-28-03, 07:39 AM
R
Banned. Rule And/Or Policy Violation
Join Date: Nov 2001
Location: USA
Posts: 1,875
Received 0 Votes on 0 Posts
The biggest problem with recess lighting is the rough opening for the fixture. There is usually a metal or plastic ring that covers the gap between the ceiling and the fixture. This is usually the source for condensation above this area and contributes to the discomfort experienced in the rooms that have these type of fixtures in both the summer and winter. There are other concerns, too many to enumerate.

The way to correct this problem is to remove the ring. Tape a piece of plastic at the 4 cornors of the plastic to the ceiling under the fixture and let it droop in a way that it still allows you access to the fixture. Basically the plastic is a drip clothe. Use spray foam in a can to to fill in the gap between the ceiling and the fixture. Let dry according to the instructions on the can and then trim off excess with a knife. Re-install ring.

In the attic put the batt insulation up to the fixture and then fill in the rest with pieces of the same insulation. You can cover the IC fixture if you like. This should cool off the room quite a bit and make it more comfortable in the winter. A conservative estimate on energy saving both heating and cooling is 10%.

Attic fan ventilation, bigger is not better. In fact it is worse. When considering attic fans one has to consider attic vents size. For example, a fan sized at 3000 cubic feet per minute (cfm) and your vents can only move 2000 cfm, the fan will burn out within a brief period of time. Most attic vents in New Jersey homes are sized a little bit less than 2000 cfm. The recommended size for attic fans in NJ is 1800 cfm that are thermostatically controlled and set at 115 degrees Fahrenheit.

There are several reasons for this. The dominant heat transfer mechanism in the summer is radiant heat transfer. Basically all that means is objects like you roofing wood members, shingles and insulation in the attic get hot and retain heat. The hotter an object gets the more heat that object will radiate. This is how the heat is transferred into the home from the attic. So the best way to address the effects of radiant heat transfer is not to allow these objects of the roofing structure to get hot. Believe or not tree shading can reduce cooling costs up to 50%. Most homes today do not have these large trees shading their homes, but think about it and if you decide to do some landscaping consider incorporating trees in the design. It may take years to reap the benefits but landscaping does have other benefits such as deterring the effects of wind pressure on the home.

The next best thing to do to reduce the heating of the objects of the roofing structure is light colored shingles. This usually reduces cooling costs by at least 15%. Your comfort and energy costs are inverted. Meaning to say as you lower your energy costs for either heating or cooling, your comfort increases proportionately.

The next action taken and the most common are attic fans. The effects of the sun beating down on your roof is so great, it is literally impossible to reduce the temperature of that roof below 115 degrees Fahrenheit. In other words setting the thermostat on these fans below 115 degrees has no affect or benefit. In fact it increases the cost of operation. The way these systems work is through convective heat transfer and Equilibrium Relative Humidity (ErH%). Air at a lower temperature will extract heat from other air and objects through movement of this air and vice-versa. The same is true with humidity where air with a lower humidity level will extract humidity from other air and objects at a higher humidity level through movement of this air. The attic fan induces the movement thereby extracting the heat and humidity in the air and objects in the attic with air from the outside. A contributing factor with radiant heat transfer is that humid air can hold more heat than dryer air. This does basically 2 things for you, one is that it reduces the temperature of the air and objects in the attic and the other is it reduces the amount of heat retained in the air and objects in the attic through convective heat transfer.
 
  #3  
Old 05-28-03, 09:27 AM
A
Member
Thread Starter
Join Date: Mar 2003
Location: Central NJ
Posts: 137
Received 0 Votes on 0 Posts
Thank you for your reponse. I am stil unclear if you should staple batts to joist or just lay them down. My attic already has insulation although it is old and torn in several places. I think I don't want to remove it but just use new R-30 batts over existing insulation. should I use faced or unfaced batts?
 
  #4  
Old 05-28-03, 10:13 AM
R
Banned. Rule And/Or Policy Violation
Join Date: Nov 2001
Location: USA
Posts: 1,875
Received 0 Votes on 0 Posts
If you lay the insulation over the old insulation it must be UNFACED. If you remove the old insulation and install all new insulation, it must be FACED.

When install insulation that will be higher than the attic floor joists, it is best to install it in layers. Install the first layer to the floor joists height and then install the next layer to your desired R-value perpendicular to the floor joists.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: